Research On Mechanism Of Performance Enhancement Of Organic Light-emitting Diodes By SiO₂ Coated Ag Nanocubes

Organic light-emitting diodes?OLEDs?have been widely considered as one of the most promising devices for the future application in the field of flat panel display and made great development because of their low power consumption,high brightness,and low cost.In the past years,red and green OLEDs have made great breakthroughs on the efficiency and lifetime to meet the basic requirements of full color display.However,the efficiency and lifetime of blue OLEDs are generally at a low level due to the few species of high-efficiency blue light materials.Therefore,the preparation of high efficiency blue Organic light-emitting diodes has always been a research hotspot and difficulty in the field of OLED.Metal nanoparticles are considered to be an effective method to improve the performance of OLED devices due to their surface plasmonpolaritons?SPP?.By adoping nanoparticles to the OLED device,the shape and size of the nanoparticles can be selected to match the LSPR resonance wavelength with the exciton emission wavelength,thereby improving the luminous efficiency and finally optimizing the device performance.In this paper,the silver nanocubes with a cubic length of 40 nm and a yield of up to 90%was prepared by improving the ethylene glycol reduction method.Then,we caoated the silver nanocubes with silica to form core-shell structure,and the ratio of reactants was adjusted.Finally,we obtained the thickness of the SiO₂ shell as 7 nm,15 nm and 20 nm.Next,we prepared a blue Organic light-emitting diode by solution method and adoped the silver nanocubes into the the emission layer.By studing the effect of silver nanocube concentration on device performance and found that when 6%volume concentration of silver nanocubes was added,the current efficiency of the device was maximized by 9.5 cd/A,being nearly 2 times of that of the device without Ag NCs.In order to improve the performance of blue OLEDs by adoping silver nanoparticles,vapor deposition method is used to prepare blue OLED devices,and silver nanocubes were adoped at the interface between the hole transporting layer and the emission layer.By studing the effect of the SiO₂ shell thickness of the silver nanocubes and the LSPR between silver nanocubes and excitons in the exciton recombination zone of the emission layer.We found that SiO₂ shell thickness determines the distance between silver nanocubes and excitons,while the exciton recombination zone determines the number of luminescent excitons around the silver nanocubes,both of which are important for influencing the surface plasmon polaritons.Finally,we prepared a blue OLED by adoping the silver nanocubes coated with 15 nm SiO₂ shell and an bipolar host material of 2,6-bis?3-?carbazol-9-yl?phenyl?pyridine?26DCzPPy?.The optimized device structure is ITO/PEDOT:PSS?45 nm?/Ag@SiO₂ NCs:26DCzPPy:FIrpic?70 nm?/TmPyPb?45 nm?/LiF?0.8nm?/Al?100 nm?.The maximum peak current efficiency of the blue OLED with Ag NCs reaches to57 cd/A,being nearly 2 times of that of the device without Ag NCs.